The production of steel in Basic Oxygen furnaces as well as other vessels for producing steel normally requires a layer of purifying slag comprised of lime and other materials which act as a blanket on top of the molten steel, encouraging various impurities in the steel to take "refuge" in the slag. The similarity is comparable to cream floating to the top of milk.
As the steel reaches the proper temperature and chemistry to "tap" into a ladle for dispatch to "teeming" continuous casting or other distribution, the tilting of the furnace will allow the slag blanket or layer to reach the taphole first before the molten steel. This would allow the slag with the impurities included to reach the bottom of the ladle (or awaiting receptacle) first, followed by the molten steel which, similar to milk and cream, would then cause the slag to permeate through the increasing level of molten steel striving to reach the top of the steel where traditionally it has tended to form a thermal blanket to retain latent heat of the steel in the ladle or other container.
In response to requests to devise some way that would in effect temporarily plug the taphole long enough for the molten steel to arrive at the taphole before too great an amount of slag had exited, my invention as hereinafter described has presented a device and method of doing so.
With experience derived from protecting my Patented devices for sampling molten metal with paper sleeves, I looked first toward paper products of a generally conical shape. Papier-mache containers used in flower shops promised such a shape in a moderate cost area. By dipping these containers in high temperature refractory slurry and filling with paper dust, sawdust, wood fiber aggregate, and glue, a composite material or mass was developed that imparted a highly thermal resistant material which was capable of adhering to the interior and external surfaces of the paper containers.
To assist in insertion, the devices or plugs centered around a paper tubular shape which provided a socket for insertion of a pipe, a pole, rod or tube, which could then extend the plug to the point where it is inserted into the taphole of the furnace, similar to forcing a cork into a bottle opening. As the opening of the taphole changes dimensions, shape, and contour with the passage of each heat of steel, the taphole plug must either lend itself to conforming to the irregularity of each opening by its very resiliency; hence, the container of the plug or device is preferably only partly filled. Various major and minor diameters and degrees of conical taper may be provided to accommodate the changing dimensions and shapes of the tapholes.
As an irregular surface on the paper is apparently necessary to provide cohesion on the surface area to the refractory slurry, the papier-mache surface has proven to be ideal, but this constitutes only one of several approaches. Abrading the surface of the paper, applying absorbent paper or fabric such as cheese-cloth with mastic are other modifications or methods of providing a surface or surfaces to which a refractory will adhere.
As the result of an investigation, attention is directed to a U.S. Pat. to Imberti, No. 3,938,791, issued Feb. 17, 1976; a Japanese Pat. No. 52-32604 having an issue date of August 1977; a Russian Pat. No. 234,803 dates 1969 and another No. 673825 dated 1979.